This invention refers to bag-filling machines, of the type in which a continuous strip or web of material, for example a strip of plastic material for making bags, is fed around and along a vertically disposed tubular guide member, at the lower end of which the individual bags are formed. The bags are subsequently filled with loose material. In particular, the invention aims to improve the devices for advancing and feeding the strip material for forming the bags, along the tubular guide member.
In bag-filling machines currently in use, the material to be packed into bags, is fed in bulk form by means of a vertically disposed tubular member which also serves as a guide for a strip of material to be made into bags, which is fed forward step by step or by pre-established lengths sufficient to make the individual bags which are automatically filled and sealed by welding.
The step by step forward movement of the strip material to form the bags, is achieved by means of revolving or rotating members, for example, in the form of two opposing toothed belts which rest constantly against the strip material and on the tubular guide member. The belts are made to rotate discontinuously, starting and stopping them repeatedly, each time a bag is made, thus subjecting the mechanical members supporting the belts to frequent and sudden starting and stopping phases. The intermittent control systems currently in use are consequently extremely delicate in that they require clutch engaging systems or other types of systems which are liable to break down or to wear out very rapidly, thus limiting the output of the bag-filling machines. These systems become even more critical in the case of high outputs where the control members are subjected to greater stress; moreover, they have a limit beyond which it is not easy nor advisable to further increase the output.
As one bag-filling machine can be used for producing bags of various dimensions which require tubular members of different diameter for guiding the strip material, it is necessary each time to carry out the operations of adjusting the position of the strip feeding members, with a consequent waste of time and slow-down in production.
A scope of this invention is to provide a step by step feed device for feeding a strip material to be made into bags, in bag-filling machines, which is capable of overcoming the drawbacks of the known devices. In particular, a scope of this invention is to provide a device as mentioned previously, which is simple and sturdy in structure, in which the control mechanisms destined to be frequently stopped and restarted have been completely eliminated, thereby substantially reducing the possibilities of breakdowns and at the same time increasing the reliability of the entire bag-filling machine.
A further scope of this invention is to provide a step feeding device of the aforementioned kind, which is capable of operating at high speeds and, therefore, of considerably increasing the output, with respect to the currently known devices.
A still further scope of this invention is to provide a device as mentioned previously, which is capable of adapting automatically to tubular guide members of different diameters, without having to carry out any adjustment whatsoever.